optimized images with ImageOptim

Ran ImageOptim, "Saved 30.8KB out of 60.7KB. 45.1% per file on average (up to 69.7%)"
![screen shot 2013-12-21 at 9 39 16 pm](https://f.cloud.github.com/assets/1312687/1797195/dbc5b9a4-6aba-11e3-87c8-a36e9a9dba63.png)